National Parks are only a sliver of a small fraction of the public govt run campgrounds in the US. Are you honing in strictly on NPs?
Either way, in general, you should be good with backing and Jack knifing trailers anywhere, not just NPs.
If there's any skepticism there, a shorter Moho and toad are the easy button for fitting into campsites. You can't make a truck and TT shorter until the TT is parked.
Pretty much any modern setup. Crew cab full size anything and any square box TT (leaving out the teardrop type little campers) will but you at 40' combined length as you've seen.
Go find a 20-24' trailer and drag it around for some experience and see how comfortable you are with it is my suggestion.
